Liquid laundry detergents provide the same performance benefits as powdered detergents such as whole wash cleaning, whitening, antiredeposition and odor removal, while providing additional benefits such as convenient dispensing, complete solubility and improved stain removal on localized stains. The improved localized cleaning is accomplished by pretreating the stain directly without the need to make a paste as with powder detergents. Liquid laundry detergents have become increasingly popular in recent years due in large part to these advantages over powders.
Liquid detergents encounter formulation difficulties over and above those seen in powders largely due to the desire to keep a wide variety of surfactants, builders and other cleaning agents solubilized for long periods in a homogeneous free flowing form. Many of the chemicals available and desirable for use in liquids are physically as well as chemically incompatible. Much of the skill utilized in formulating liquid detergents goes into keeping these chemicals stable for long periods in intimate contact with incompatible materials.
Over the last ten to twenty years, the addition of enzyme to laundry detergents for stain removal has become commonplace, particularly in Europe. Many laundry detergents now contain one or more proteolytic and/or amylolytic enzymes to improve their performance on stains that are either protein- or starch-based, such as those caused by blood, milk, grass or fruit juices. Incorporation of enzymes into powder detergents has become common, since in powders the enzymes are not in intimate contact with surfactants and other chemicals which cause degradation of the enzyme and consequent loss of enzyme activity as well as decreased effectiveness.
Incorporation of enzymes into liquid detergents remains a difficult problem despite significant improvements in enzyme stabilizing systems. The problem of enzyme stability is increased in high pH systems since the product pH acts to destabilize most common proteolytic enzymes. Many liquid laundry detergents now in the marketplace incorporate enzymes in the formulation. In all cases of which we are aware, the product pH is 8.5 or less.
Many non-enzyme liquid laundry detergents have pH's of 9.0 or greater. A high product pH is desirable because alkaline liquids give improved performance on fatty soils, both in concentrated form during pretreatment with the neat liquid, and in the wash solution where it is used at a concentration of about 0.2%. Wash solution pH's of 8.5 or greater permit improved whole wash detergency on fatty soils by saponifying the fatty materials to form an easily removed soap. Improved performance on both proteinaceous and fatty soils would result from an enzyme-containing, high pH liquid. Furthermore, because fatty soils lower wash solution pH, liquid detergents which resist drops in wash solution pH are preferred. This resistance to lowering of wash solution pH in the presence of fatty soils results from the buffering capacity provided by the detergent.
To date it has been difficult to incorporate a proteolytic enzyme in a high pH liquid and maintain acceptable enzyme stability over the long storage periods that result during the production, distribution and sale of the product.
Liquid laundry detergent systems containing some of the features described by our invention are contained in the patent literature.
Hora et al. U.S. Pat. No. 4,261,868 discloses the use of an enzyme in a high pH (7.5 to 11.0) liquid laundry detergent with a stabilizing system including a polyfunctional amino compound (such as triethanolamine) and borax. Anionic to nonionic surfactant ratios of 1:1 to 1:10 are disclosed. Example 1 includes sodium tripolyphosphate, dimethyl glycine and Alcalase.RTM. enzyme and is said to have a pH of 10.0.
Boskamp U.S. Pat. No. 4,462,922 discloses the use of a high alkaline enzyme in a liquid laundry detergent along with a stabilizing system including borax, a reducing alkali metal salt and a polyol and/or a polyfunctional amino compound. The pH of the '922 composition is said to be near neutral, preferably from 8.0 to 10.0. According to the '922 patent, the composition can be buffered to a value within that range by addition of a suitable buffer system. The pH of the wash liquor is said preferably to be 1 pH unit higher at an in-use concentration of 1%. Boskamp uses the reducing alkali metal salt to provide effective enzyme stabilization.
Boskamp U.S. Pat. No. 4,532,064 teaches the use of a high alkaline enzyme having a maximum activity at pH 8-12 in a liquid laundry detergent along with a stabilizing system including borax, a reducing metal salt, an optional buffer, and the use of a dicarboxylic acid as replacement for the polyol or polyfunctional amino compound. The pH of the final composition is near neutral, preferably 7.5 or higher and may be buffered to a value in that region by addition of a suitable buffer system. The pH of the wash water is about 1 pH unit higher at an in-use concentration of 1%. The pH of Example 1 is 7.5.
Letton et al. U.S. Pat. No. 4,318,818 discloses the use of an enzyme in a liquid laundry detergent with a stabilizing system comprising a polyol, calcium and a short chain carboxylic acid. Mono-, di-, and triethanol amines may be used as pH buffers. While Letton et al. disclose a potential product pH range of from 6.5 to 10, they prefer a range of from 7 to about 8.5 to obtain a combination of enzyme stability and detergency.
Example XIII E of Letton et al. includes Maxatase, surfactant, ethanol, sodium formate and triethanolamine, and is said to have a pH of 9.6. Example XIII P includes surfactant, ethanol, Maxatase, sodium carbonate, and sodium formate and is said to have a pH of 10.0.
Tai U.S. Pat. No. 4,404,115 teaches the use of an enzyme in a liquid laundry detergent with a stabilizing system including a polyol (optional), an alkali metal sulphite and an alkaline metal pentaborate. The pentaborate is said to provide a buffering effect on its own at the optimal pH condition to the liquid composition which on dilution in use gives a sufficiently alkaline pH for optimal detergency. The pH of the Tai wash liquor on use of the composition is said to be in the alkaline range of well above 8 at an in-use concentration of about 1%. Example III(6) discloses a metaborate and enzyme-including composition which has a pH of 11.36 and a 1% solution pH of 9.26 but an enzyme stability after 2 weeks of 10% or less. Other ingredients include surfactants + triphosphate builder.
While Tai recognizes the importance of a high wash solution pH, he generally formulates near neutral neat liquids, thus losing the pretreatment benefit of our invention. Additionally, he teaches the use of a pentaborate rather then tetraborate (borax) (page 2, line 5).
Inamorato et al. U.S. Pat. No. 4,652,394 teaches the use of an enzyme in an aqueous laundry detergent with an enzyme stabilizing system including propylene glycol and borax. Inamorato fails to recognize the use of a high pH liquid for fatty soil removal.
In each instance cited, the prior art patents apparently fail to recognize at least one or more critical components which in combination provide the benefits of improved pretreat and whole wash efficacy on fatty soils as well as maintaining the necessary enzyme activity for removal of enzyme-susceptible stains.
The desirability of combining the properties of high alkalinity levels and inclusion of enzymes in detergent products has led to the development of alkaline protease enzymes that are specifically designed to deliver peak effectiveness in wash solutions of pH 8.5 and higher. Many powder detergents now include both high alkalinity sources and enzymes designed to function primarily in high wash solution pH systems. This has allowed the powder detergents to provide maximum benefits for detergency in two areas of primary concern to the consumer. The problem to date has been to combine these two highly desirable properties in a liquid detergent. In a high alkalinity liquid detergent enzymes are in solution at high product pH (&gt;9.0). The high product pH is known to be detrimental to the enzyme stability over the long time periods (often at elevated temperatures) that are seen in normal product storage. We have provided a liquid detergent system which delivers the two aforementioned performance benefits while still retaining sufficient enzyme stability for effective stain removal.
Our invention involves the stable incorporation of enzymes in a high pH liquid laundry detergent and the resultant improvements in detergency on both enzyme-susceptible and fatty soils. It is the stable inclusion of the specified levels of titratable alkalinity in conjunction with an enzyme stabilization system utilizing glycols, calcium and/or borax resulting in improved proteolytic enzyme performance and excellent fatty soil removal (both in the whole wash and in pretreat usage) that forms the basis of our invention.